Finished lubricants used for automobiles, diesel engines, axles, transmissions, and industrial applications consist of two general components, a lubricating base oil and additives. Lubricating base oil is the major constituent in these finished lubricants and contributes significantly to the properties of the finished lubricant. In general, a few lubricating base oils are used to manufacture a wide variety of finished lubricants by varying the mixtures of individual lubricating base oils and individual additives.
Lubricating base oils are usually prepared from hydrocarbon feedstocks having a major portion boiling above 650° F. Typically, the feedstocks from which lubricating base oils are prepared are recovered as part of the bottoms from an atmospheric distillation unit. This high boiling bottoms material may be further fractionated in a vacuum distillation unit to yield cuts with pre-selected boiling ranges. Most lubricating base oils are prepared from that fraction or fractions where a major portion boils above about 700° F. and below about 1050° F.
Although lubricating base oils traditionally have been prepared from conventional petroleum feedstocks, recent studies have shown that high quality lubricating base oils can be prepared from unconventional waxy feedstocks, such as from slack wax and Fischer-Tropsch wax. Since these unconventional waxy feedstocks are primarily composed of normal paraffins, these feedstocks initially have poor low temperature properties, such as pour point and cloud point. In order to improve the low temperature properties of the waxy feedstocks, selective branching must be introduced into the hydrocarbon molecules, as for example, through hydroisomerization. See, for example U.S. Pat. Nos. 5,135,638; 5,543,035; and 6,051,129. While hydroisomerization may be used to produce premium lubricating base oils from waxy feedstocks, the process conditions at which the reactor must be operated also results in considerable cracking. Cracking of the hydrocarbon molecules during the hydroisomerization operation results in a significant yield loss among those hydrocarbons boiling in the range of lubricating base oil. At the same time cracking increases the yield of lower boiling hydrocarbons, such as diesel and naphtha, which are of lower commercial value. Operating under less severe conditions, as for example at lower pressure, results in less cracking and higher yields of lubricating base oils. However, operating at lower pressures also results in accelerated deactivation of the catalyst which significantly shortens the run life of the hydroisomerization catalyst. The present invention is directed to a hydroisomerization process using a novel catalyst combination which allows the hydroisomerization reactor to be operated at a low hydrogen partial pressure without the typical deactivation problem associated with low pressure operation. This translates into longer catalyst run life while at the same time achieving less cracking and higher lubricating base oil yields.
As used in this disclosure the word “comprises” or “comprising” is intended as an open-ended transition meaning the inclusion of the named elements, but not necessarily excluding other unnamed elements. The phrase “consists essentially of” or “consisting essentially of” is intended to mean the exclusion of other elements of any essential significance to the composition. The phrase “consisting of” or “consists of” is intended as a transition meaning the exclusion of all but the recited elements with the exception of only minor traces of impurities.